Analysis of stamping production molds
Stamping is one of the practical processes for the production of high-volume parts. In the stamping production process, the mold has the most problems, which is the most important factor in the entire stamping production factor. It has a direct impact on productivity and costs. Affect the lead time of the product. Mold problems are mainly focused on mold damage, product quality defects and mold sharpening, which have long plagued industry production. Only these few key points can be handled correctly. Stamping production can proceed smoothly.
1 Mold failure
Mold failure is the most common problem in stamping production, often causing production stoppages and affecting the product production cycle. Therefore, it is necessary to find the cause of the mold failure as soon as possible and repair it reasonably.
1.1 The mold is damaged
Mold damage refers to mold cracking, breaking, opening, etc., to deal with mold damage problems, it is necessary to find the cause from the design of the mold, manufacturing process and mold use.
First of all, it is necessary to check whether the manufacturing material of the mold is suitable and whether the corresponding hot embedding process is reasonable. Usually, the heat treatment process of the mold material has a great influence on it. If the quenching temperature of the mold is too high, the quenching method and time are unreasonable, as well as the number of tempering and temperature, improper selection between the elbows, will lead to damage after the mold enters the stamping production. The size or depth design of the blanking hole is not enough, which is easy to block the slot hole and cause damage to the blanking plate. The spring force design is too small or the contour sleeve is not of equal height, which will break the spring and tilt the blanking plate. Cause overlapping punching and damage to parts. The punch is improperly fixed or the screw strength is not enough. This can cause the punch to fall or break.
When the mold is used, the part position, orientation, etc. are installed incorrectly or the bolt is not well tightened. The working height adjustment is too low, and the guide column lubrication is insufficient. Faulty feeding equipment, abnormal presses, etc., will cause damage to the mold. If foreign objects enter the mold, parts overlap, scrap blockage and other situations are not dealt with in time, and the processing and production continue, it is easy to damage the blanking plate, punch, lower template and guide column of the mold.
1.2 Card mold
During the stamping process, once the mold is inflexible or even stuck, it is necessary to stop production immediately, find out the cause of the mold, and eliminate the fault. Otherwise, the fault will be amplified and the mold will be damaged.
The main reasons for jamming are: poor mold guidance and tilt. or there is a foreign object between the templates, so that the templates cannot be flattened; The mold strength design is not enough or the force is uneven. Cause mold deformation, such as the hardness and thickness design of the mold base and template are too small, and it is easy to be deformed by external forces; The mold position is not installed accurately, and the positioning error of the upper and lower molds is out of tolerance. or the accuracy of the press is too poor, so that the mold interferes; The strength of the punch is not enough, and the position of the large and small punches is too close, so that the lateral force of the mold is unbalanced. At this time, the strength of the punch should be increased to enhance the guidance protection of the discharge plate.
1.3 Mold damage and repair
The cost of molds for stamping production is high. Usually the mold fee accounts for 1/5-1/4 of the total cost of the part. This is because, in addition to the difficulty and high cost of mold manufacturing. The cost of mold repair and sharpening maintenance after production is also high, and the original cost of the mold only accounts for about 40% of the entire mold cost. Therefore, timely maintenance of the mold and prevention of mold damage can greatly reduce the cost of the mold for stamping production.
After the mold is damaged, there is also the question of the choice of repair and scrap. Generally speaking. Unnatural wear failure of stamping dies, such as the failure of non-critical parts. As well as small punch breakage, punch upsetting rough shortening, concave template cracking, punching edge cracking and other failures. Most of them can be fully restored to normal condition by repair and put back into stamping production. But. When the key parts of the mold are seriously damaged, sometimes the convex and concave dies are damaged at the same time. The one-time repair cost exceeds 70% of the original cost of the die, or the mold life is near. Then the significance of maintenance is not much, and scrapped molds should be considered: in addition to large molds and continuous molds with complex structures. When the mold maintenance technology is too complicated, the cost of mold repair is too large, and the difficulty will inevitably make the maintenance cycle too long, seriously affecting the normal production of stamping, you should choose to fail and scrap in advance and remanufacture the mold.
Under normal circumstances, the main form of die failure is excessive wear. Delivery from new mold manufacturing. Until the burr of the punched parts exceeds the standard, the size and shape accuracy of the parts are out of tolerance, and the mold can no longer be repaired or has no repair value at all, the mold can only be scrapped. From the commissioning of a new mold to the end of failure. Generally, it is repaired and sharpened many times.
2 Parts quality defects
The most common defect in part quality is the product size out-of-specification. Only a few products have surface quality issues.
2.1 Size out-of-specification
Dimensional out-of-tolerance is a serious defect in stamped parts. In this regard, the first thing to check and check the design of the mold is to eliminate the reasons for design and manufacturing. If the out-of-tolerance size is related to the thickness of the material, the thickness of the stamping material and the material and hardness should be tested.
The size is out of specification caused during the stamping production process, mainly due to the wear of the mold, poor positioning guidance and deformation of the part. The cutting edge of the mold is worn. It will cause the burr to be too large or the cutting size becomes larger, the punching hole becomes smaller, and the flatness is too poor, and the mold should be sharpened or replaced. Poor positioning guidance includes no guide, guide pin or other positioning device does not work, the feeder is not relaxed, the positioning block is worn so that the feeding distance is too long, the length of the guide plate is not correct, or the guide gap is too large. The parts are deformed in production, mainly impact deformation, such as the blowing air pressure of the product is too strong or the gravity falls and the impact is too deformed: when discharging is squeezed or deformed, the discharging position should be cleaned up in time or the discharging space should be increased: improper deformation of ejection. For example, if the ejector pin is improperly arranged, the spring force is inappropriate or the ejection is too long, the spring force should be adjusted or the position or pin quantity should be changed; Blanking deformation. Some bent parts cannot allow the material to overlap, and must fall down every time, and when the disc strain occurs, the pressure pad can be used to eliminate it; Punching and shear deformation, mainly the material distortion is uneven. increased size or asymmetrical center; Chip extrusion deformation is due to the extrusion deformation of scrap floating or fine chips left on the die surface or foreign matter.
2.2 The surface quality is unqualified
The surface quality problems of the stamped parts are mainly excessive burrs. The cause of excessive burrs of parts is, first of all, the wear of the mold edge, and the mold should be re-ground (described below) to ensure that the cutting edge is sharp. Secondly, the interval of convex and concave dies is unreasonable, most of the gaps are polished on the side of the ambassador, the gap is too small and there will be a secondary shear surface, if the material hardness is too high, the material should be replaced or the gap should be increased. When the size of the blanking edge is too small or the cutting edge material is too small, the material is pulled into the mold gap and becomes a burr. At this point, the size of the blanking edge or the margin of cutting must be increased.
3 Sharpening of the mold
Reasonable sharpening of the mold in stamping production. It can effectively improve the life of the die, save the cost of the mold, and greatly reduce the cost of the product.When the cutting edge of the
die is worn to a certain extent, the originally sharp edge becomes dull, which will cause the burr of the blanking part to be too large, and the size and shape accuracy will decrease. Therefore, the mold must be sharpened to restore its sharp punching edge. Reduce punching burrs and dimensional and geometric deviations, and improve the surface quality of formed parts. If the mold is not sharpened in time, it will delay the sharpening time, so that the already blunt edge is subjected to stiff, too large, too thick burr severe friction, forming a vicious cycle of excessive wear of the mold, resulting in several times the sharpening amount to restore the sharpness of the edge, greatly shortening the life of the mold. When the burr of the part is about to exceed the allowable burr height, the production should be stopped immediately and the mold should be sharpened. In the actual production, on-site workers are accustomed to determining the size of the burr of the part and determining the timing of sharpening by feeling, so that the operation error is large. It is best to grasp the wear of the cutting edge and the degree of dullness of the cutting edge 121 by detecting the burr height and thickness of the part, the uniformity of burr distribution, the size and shape accuracy of the punching part, and the quality of the punching surface, so as to determine the best sharpening time of the mold. #p# pagination heading #e#
The amount of mold grinding must be determined according to the actual wear of the end face and sides of the cutting edge, and relevant factors such as material thickness, die shape and structure, and sharpening sequence should also be considered. After the die is sharpened for many times, the size will change, especially the punching die designed with a large conical die mouth design, due to the pouring of the wall of the die cutting edge, after sharpening the upper surface of the mold, its horizontal size will inevitably produce an increment. Therefore, before sharpening, it should be calculated according to the angle of the cone, and attention should be paid to the measured part size when sharpening, so as to prevent the product from being out of tolerance due to multiple sharpening to make the size increment of the part too large.